This invention relates to implantable medical devices, and particularly to implantable cardiac devices that are capable of storing physiological data.
Patients who have heart abnormalities often benefit from the surgical implantation of a cardiac device, such as a pacemaker or a cardioverter/defibrillator. For example, if a patient suffers from bradycardia, a condition in which a patient's heart beats too slowly, a cardiac stimulating device can be used to provide pacing pulses to the patient's heart. Other patients suffer from heart arrhythmias such as tachycardia, in which the heart beats too quickly. Many implantable cardiac stimulating devices have cardiac sensors that may be used to monitor a patient's internal cardiac signals to detect and terminate cardiac abnormalities, such as episodes of tachycardia.
Cardiac stimulating devices may also provide stimulating pulses to a patient's heart based on the patient's measured level of physical activity. Such cardiac stimulating devices, known as rate-responsive pacemakers, determine the physiological needs of the patient by monitoring the patient's physical movements using activity sensors. Various other sensors may also be used by cardiac devices either to determine the appropriate stimulating pulses to deliver to the patient's heart or to monitor the patient's condition in more detail. For example, sensors may be used to measure the patient's blood flow rate, blood oxygen level, or cardiac wall motion. Additional sensors may be used to measure the patient's internal temperature or respiration rate. Each of these sensors generates data that may be used by a cardiac stimulating device to determine the number and intensity of stimulating pulses that should be provided, or by a cardiac monitoring device to monitor a patient's physical condition.
Because cardiac stimulating devices can generally be programmed to perform various functions in response to the data measured by the various physiological sensors, the response of cardiac stimulating devices to measured cardiac signals and other physiological data can be tailored by a physician to suit the needs of individual patients. Without individually tailoring the device settings, some patients may experience discomfort if they suffer from an abnormal cardiac condition that is not detected and treated adequately by the cardiac stimulating device.
In order to determine whether a cardiac stimulating device is programmed properly, a physician can direct the device to store measured cardiac signals in memory. These signals can then be transmitted from the cardiac device to an external display device, for review by the physician. However, it would also be desirable if a cardiac stimulating device or cardiac monitoring device could be directed to store data from sensors such as a blood flow sensor, a blood oxygen level sensor, an activity sensor, a temperature sensor, a respiration rate sensor, or other physiological sensors, because data from these sensors may also affect the response of the cardiac stimulating device and may be useful for accurately diagnosing a patient's condition.
Because the memory that is available in a cardiac stimulating device or cardiac monitoring device is limited, it would be desirable to be able to direct a cardiac stimulating device to store sensor data from only certain selected sensors to conserve memory. Preferably, the physician can use an external control device to program the cardiac stimulating device or monitoring device to store data from the selected sensors. Further, it would be desirable for the patient to be able to direct the device to retain data during an episode of cardiac discomfort. Such data would be valuable to the physician for diagnosing the patient's condition and for adjusting the settings of the cardiac stimulating device to prevent further discomfort. If desired, data could also be retained automatically, when the cardiac stimulating or monitoring device determines that an abnormal physiological condition exists.